1. Field of the Invention
The present invention relates to a technique for detecting azimuth and inclination angle of a center axis of a device of interest in a terrestrial coordinate system through detection of geomagnetism components and gravitational force components, and more particularly, to a technique for improving its detection accuracy.
2. Description of the Related Art
Recently, there have been developed portable terminal devices, such as a cellular phone, which include a magnetic sensor for detecting geomagnetism and an acceleration sensor for detecting inclination of the body of the device in order to measure azimuth, in accordance with the trend of their performance enhancement. Such a device is advantageous in that accuracy of azimuth detection can be improved by means of correction based on inclination of the device body.
Conventional techniques employing such correction are disclosed in Japanese Patent Application Laid-Open (kokai) Publication Nos. H10-185608 and 2003-172633. Both the techniques use a geomagnetism sensor and an acceleration sensor, and improve its detection accuracy through coordinated operation of these sensors.
However, when a detection apparatus as disclosed in the publications is incorporated in a portable terminal device such as a cellular phone, there arises a problem in that the acceleration sensor detects an acceleration component produced as a result of movement of the portable terminal device, and the detected inclination of the portable terminal device involves an error, whereby the azimuth correction amount involves an error, and the detection accuracy deteriorates. This problem cannot be solved by the techniques disclosed in the above-mentioned publications.